JP2558325B2 - Magnetic tape recording / playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a rotary head helical scan system configured to record and reproduce video signals on the surface layer of a magnetic tape and digital audio data on the deep layer of the magnetic tape. The present invention relates to a magnetic tape recording / reproducing apparatus, and more particularly to a magnetic tape recording / reproducing apparatus adapted to control reproduction equalization (hereinafter referred to as equalizing) characteristics of a reproduction signal.

[Conventional technology]

Figure 5 shows, for example, the 1986 ICASSP draft “Research on the digitalization of audio signals in video tape recorders”.
(A STUDY ON THE DI GITIZATION OF AUDIO SIGNALS FO
It is a block diagram showing a configuration of a conventional magnetic tape recording / reproducing apparatus shown in R VIDEO TAPE RECORDER (Hitachi).
In the figure, (1) is a video signal (hereinafter referred to as video signal) recording processing circuit, (2) is a video recording amplifier,
(3) is a rotary drum incorporating a video head and an audio head, (4) is a magnetic tape, (5) is a video head amplifier, and (6) is a video signal reproduction processing circuit.

Further, (7) is an analog-digital converter (hereinafter,
ADC), (8) digital audio signal (hereinafter referred to as audio signal) recording processing circuit, (9) offset 4-phase differential phase signal modulation circuit (hereinafter referred to as 4-phase modulation circuit), (10) ) Is an audio system recording amplifier, (11) is an audio system head amplifier, (12) is an offset 4-phase differential phase modulation signal demodulation circuit (hereinafter referred to as a 4-phase phase demodulation circuit), and (13) is a digital audio signal reproduction processing circuit. , (14) are digital-analog converters (hereinafter DAC
Is called).

 Next, the operation of the above configuration will be described.

The luminance signal of the video signal input to the video signal recording processing circuit (1) is FM-modulated, and the chrominance signal is frequency-converted to a low frequency band, and the video is incorporated in the recording amplifier (2) and the rotating drum (3). It is recorded on the magnetic tape (4) via the head. The signal reproduced by the video head is amplified by the head amplifier (5) and restored to a video signal by the video signal reproduction processing circuit (6). The above operation is the same as the operation of the home VTR such as the VHS method and the β method.

On the other hand, the input audio signal is converted into a digital signal by the ADC (7), and is converted into a pulse code modulated PCM signal by adding an error correction code and the like by the digital audio signal recording processing circuit (8), and further converted into 4 It is converted into an offset four-phase differential phase modulation signal (hereinafter referred to as QPSK signal) by the phase / phase modulation circuit (9), and is passed through the recording amplifier (10) and the audio head built in the rotary drum (3) to be magnetically transferred. Recorded on tape (4). The audio signal is recorded on the lower side of the video signal, that is, in the deep layer of the magnetic tape (4), like the VHS type Hi-Fi audio signal. Further, the signal reproduced by the audio head is amplified by the head-up (11), the PCM signal is restored by the 4-phase phase demodulation circuit (12), and the digital audio signal reproduction processing circuit (13) performs error correction or the like. Processing is performed and the audio signal is restored by the DAC (14).

Here, the operation of the digital audio signal processing circuit (8) and the four-phase modulation circuit (9) will be described in more detail with reference to FIGS. 6 to 13.

In the rotary head type magnetic recording / reproducing apparatus, the PCM signal is recorded in a format of a format corresponding to the switching cycle of the rotary head. An example of this is shown in FIG. The PCM signal is composed in video field units, and one block consists of 4 blocks of preamble, 134 blocks of DATA, and 3 blocks of postamble, for a total of 141 blocks.

FIG. 7 shows a detailed structure of the digital signal recording processing circuit (8) shown in FIG. 5, in which the digital audio signal is added with an error correction code by the PCM data generator (15) and shown in FIG. Converted to DATA block PCM signal. On the other hand, data of a specific pattern that facilitates the carrier signal and data clock playback operation during QPSK signal playback is stored in the memory (16).
It is output as a PCM signal of the preamble and the postamble of FIG. PCM data generator (15), memory (1
6) and the data selector (17) are controlled by the control circuit (18) which receives the sampling signal FS of the audio signal, nFS related to the data clock FCL, the clock signal mFCL and the rotary head switching signal AH-SW signal. It

FIG. 8 shows the detailed structure of the four-phase phase modulation circuit (9) shown in FIG. 5, in which the PCM signal and the data clock FCL are shown.
Is a D-type flip-flop (hereinafter called D-FF)
In the serial-parallel converter (20) composed of (21) to (23), the data clock FCL of 2.6MHz is divided by 1/2 to 1.3MHz.
Clock signal Is divided into P data and Q data at the rising and falling edges of P and Q data. Next, the P data and Q data are respectively non-otherwise OR gates (hereinafter referred to as EX-OR) (31), (33) and D-FF. (3
2) Differentially encoded by the differential encoder (30) composed of (34) and converted into p-data and q-data. FIG. 9 shows how the P, Q data and p, q data are converted when the PCM data is 00110011 ... (Hereinafter referred to as "0011" type.). Both p-data and q-data It becomes a rectangular wave with a period of, and its spectrum spreads to the high range as shown by the circle in Fig. 10.
A low-pass filter as shown in (hereinafter referred to as LPF).
After the signal is band-limited by and is converted into a signal having a spectrum shown by a mark, the carrier signal generator (37) generates, for example, a 2.5 MHz carrier signal FC together with balance mixers (41), (42) and an adder ( 43) and 90 ° phase shifter (44)
Is input to a four-phase transfer modulator (40) which is modulated. The spectrum of the offset four-phase differential phase-modulated signal QPSK is shown in the figure on page 64 of "Basics of Digital Modulation Circuit" (Ohm Co. 1984) for random signals.
The spectrum is as shown in 4.7, FC = 2.5MHz, FCL =
In the case of 2.6MHz (2.6Mbps) As shown in Fig. 11, there is a spread of about ± 0.65MHz around FC. On the other hand, the "0011" type
Since the p-data and q-data of the PCM data have the spectral structure as shown in FIG.
− When modulated with data, the QPSK signal spectrum is Has a unique spectral component such as. Since the above p-data leads the q-data by 45 °, QP in this case
The spectrum of the SK signal is as shown in Fig. 12. It is about 8 dB larger than the component. Next, in FIG. If p is the opposite phase, p-data and Q-data will be exchanged, and accordingly p-data and q-data will also be exchanged, so they will be called p'-data and q'-data respectively. . Since the p'-data is delayed by 45 ° from the q'-data, the spectrum of the QPSK signal in this case is opposite to that of FIG. 12 as shown in FIG. The ingredient is better It is about 8 dB smaller than the component. As mentioned above,
The characteristic of the offset four-phase differential phase modulation is that the differentially encoded data is different even for the same PCM data and thus the spectrum of the QPSK signal is different. The QPSK signal spectrum when modulated with a random signal is shown in FIG.
It is shown by QPSK in FIG. The above QPSK signal may interfere with the video system or cause cross modulation.
Bandpass filter BPF for components below 1MHz and above 4MHz
After being removed by (45), it is output as a REC-QPSK signal.

Next, the four phase modulation circuit (9)
The reproduction and demodulation of the QPSK signal will be described in more detail with reference to FIGS. 14 to 18.

FIG. 14 shows the detailed structure of the 4-phase phase demodulation circuit (12) shown in FIG. 5, and the reproduced QPSK signal (PB-QPSK).
Is played back and equalized by the playback equalizer (50) EQ-Q
It becomes a PSK signal, and is further demodulated as a PCM signal by the synchronous detection circuit (51), the carrier reproduction circuit (52), the clock reproduction circuit (53), and the data reproduction circuit (54). This operation is performed by, for example, "a direct satellite broadcast PCM audio demodulator" (Nationa
l Technical Report Vol.30 No.1 Feb.1984) 6th P15
Reproduction of P and Q data by the synchronous detection method shown in the figure and reproduction of carrier signal by the inverse modulation method and digital phase comparison type clock signal reproduction shown in Fig. 15 of P19 are performed. In the reproduction circuit (54), signal processing such as differential decoding and parallel-serial conversion is performed to restore the original PCM signal.

Next, reproduction equalization of the QPSK signal will be described. The QPSK signal has a spectral shape as shown by QPSK in FIGS. 12 and 13 or “REC” in FIG. 15. Such a QPSK signal is transmitted to the audio recording amplifier (10) and the rotary drum (3). The output of the audio head amplifier (11) is shown as "PB1" or "PB2" in Fig. 15 when recording / playback is made up of the built-in audio head, magnetic tape (4), and audio head amplifier (11). A low-frequency emphasis / high-frequency suppression type spectrum shape is obtained. A reproduction equalizer (50) is used to restore the spectrum of the reproduced signal to the spectrum at the time of recording so that the offset four-phase phase demodulation operation is correctly performed.
The characteristics shown in "EQ1" and "EQ2" in Fig. 16 are given to "1" and "PB2".

Since the above QPSK signal is recorded in the deep layer, it is partially erased by the video signal recorded in the surface layer later, and the erasure is more in the high frequency side signal, and further it is erased depending on the magnitude of the video recording current. However, the spectrum of the QPSK signal recorded on the magnetic tape (4) is not always constant. In the case of a home VTR that has a standard mode and a long time mode such as a triple mode as a recording mode, not only the track width of the audio signal recorded on the magnetic tape (4) but also the track width of the video signal is different,
As a result, the spectrum of the QPSK signal recorded in the deep layer changes greatly, and accordingly, the spectrum of the reproduced PSK signal also differs. The spectra indicated by “PB1” and “PB2” in FIG. 15 are examples of the reproduction spectra in the standard mode and the long-time mode, respectively. The reproduction spectrum of the PSK signal also changes depending on the characteristics of the audio head and the characteristics of the video head. In addition, the conditions become more complicated when reproducing a magnetic tape recorded by another VTR. Therefore, automatic control (adaptation) of the characteristics of the reproduction equalizer is essential.

A phase linear equalizer having a flat group delay characteristic is generally used as the reproduction equalizer (50).

FIG. 17 shows an example of an adaptive reproduction equalizer based on a phase linear equalizer, which is based on the inventors' prior application (Japanese Patent Application No. 62-205518).

First, the operation of the reproduction equalizer (50) will be described. This equalizer is a delay element (60) with a constant delay time.
~ (63), adder (64), (65), coefficient circuit (66) ~
(68) and adder (69), the amplitude characteristic G
(Ω) is G (ω) = K0−K1cosωτ + K2cos2ωτ (1) where ω = 2πf. Therefore, coefficient circuits (66), (67), (68)
, That is, the gains (K0), (-K1 / 2), and (K2 / 2) are determined so that the characteristics shown in FIG. 16 can be obtained.

For example, the delay time of the delay elements (60) to (63) is τ = 65
nsec, coefficient of each coefficient circuit (66) ~ (68) K0 = 3.76, K1
= 4.51 and K2 = 0.94, it is almost the same at 1.5MHz to 3.5MHz.
8dB / MHz characteristics can be obtained.

Next, the operation of the characteristic control section (70) of the reproduction equalizer will be described. The PB-QPSK signal is reproduced and equalized by the reproduction equalizer (50 and becomes an EQ-QPSK signal. This EQ-QPSK signal
The signal passes through the signals in the bands indicated by "H" and "L" in Fig. 18.
BPF1 (71) and BPF2 (72) and signal level detector DET1
(73) and DET2 (74) detect the shape of the spectrum. The timing signal generation circuit (76) uses the rotation phase detection signal D-PG of the rotating drum to indicate the AH-SW signal indicating the switching of the audio head, the preamble, the PRE.AMB. Signal indicating the position of the postamble, and the PST.AMB. Signal. Is output. The coefficient control section (75) uses the above AH-SW signal, PRE.AMB signal, PST.AMB signal and DET1 (73), DET2 (74) output signal to EQ-QPSK
The spectrum shape of the DATA part where the sideband component is dispersed in the signal is detected, and the coefficient circuit is made to match the spectrum shown by EQ-QPSK in Fig. 18 with the spectrum shown by REC-QPSK (the spectrum at the time of recording). Control (66) to (68). Further, the coefficient control section (75) includes coefficient circuits (66) to (6
The numerical data for optimal control of 8) is generally prepared in advance, but it is general, and since the audio head can be identified by the AH-SW signal, the spectral shape of the PB-QPSK signal and the audio head characteristics. Regardless of the situation, the optimum playback equalization operation can always be performed and the audio signal can be restored correctly.

[Problems to be Solved by the Invention]

However, since the conventional adaptive reproduction equalizer is configured as described above, it is necessary to accurately make the bandpass filter and level detector for detecting the spectral shape, and to extract the sideband of the QPSK signal with the bandpass filter. Therefore, there is a problem that the signal level becomes small, and accordingly the reliability of the spectral shape detection is low.

The present invention has been made to solve the above-mentioned problems, and by improving the shape detection accuracy of the reproduction spectrum, optimum equalization can always be performed, and the audio tape recording / reproduction can be correctly restored. The purpose is to provide a device.

[Means for solving the problem]

The magnetic tape recording / reproducing apparatus according to the present invention is centered on the carrier frequency FC of a part of the QPSK signal of the recording track,
High and low symmetry with respect to the data clock FCL And means for indirectly detecting the spectral shape of the QPSK signal from the amplitude of the pilot signal reproduced and equalized by the reproduction equalizing means at the time of reproduction. It is characterized in that it has means for controlling the characteristics of the reproduction equalization means, and is configured to optimally control the reproduction equalization characteristics.

[Action]

According to this invention, a part of the recording track is Since the pilot signals are alternately recorded periodically, it is possible to easily determine the quality of the reproduction equalization characteristic by detecting the level of the pilot signal. Therefore, the characteristic control of the reproduction equalization means can be easily performed. Therefore, even if the spectral shape of the QPSK signal recorded on the magnetic tape differs due to the recording mode or audio channel, the spectral shape of the QPSK signal that has been reproduced and equalized becomes the spectral shape of the QPSK signal at the time of recording. It is possible to perform control so that they coincide with each other, always realize the optimum reproduction equalization operation, and correctly restore the audio signal.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows pilot data in a magnetic tape recording / reproducing apparatus according to an embodiment of the present invention. The pilot data repeats a plurality of "0011" data strings and a plurality of "0110" data strings. The <3H + 6H> type pilot data and < Two types of data, 6H + CH> type pilot data, correspond.

Next, the effect of the pattern of FIG. 1 will be described. The PCM signal generated by the digital audio signal recording processing circuit (8) is divided into P data and Q data by the serial-parallel conversion circuit (20) which constitutes the 4-phase phase modulation circuit (9).

At this time, since the P data and the Q data are simply separated every other serial data, as shown in FIG. 1 (e), the distinction between <3H + 6H> type pilot data and <6H + CH> type pilot data is made. Can not. Therefore, the <3H + 6H> type pilot data will be described.

Figure 2 shows the <3H + 6H> type pilot data.
When switching from the "3H" section to the "6H" section, Fig. 3 shows "6H"
Serial-parallel conversion circuit (2 when switching from section to "3H" section
It is a figure explaining operation | movement of 0) and a differential encoder (30). The pilot data is the data string of "0011" and "011".
It is a repeat of the data string of 0 ", this data is 2.6MHz
Data clock signal of 1.3 MHz clock signal FCL divided by 1/2 P-data and Q-data are extracted at the rising edge and the P-data and Q-data are differentially encoded into p-data and q-data, respectively. 2 and 3, p-data is a repeating pattern of 01 for "3H" section and "6H" section. Becomes a square wave. On the other hand, q-data is delayed by 45 ° with respect to p-data in the "3H" section as shown in FIG. Although it becomes a rectangular wave, it advanced 45 ° with respect to p-data by switching to the "6H" section. Then, as shown in Fig. 3, by switching from "6H" section to "3H" section, it was delayed by 45 ° with respect to p-data. Return to. The phase relationship between the p-data and the q-data is the same as the p-data and the q-data in FIG. 9 for the "3H" section, and the spectrum of the QPSK signal is the 12th.
It is the same as the figure.

Further, in the "6H" section, it is the same as p'-data and q'-data in FIG. 9, and the spectrum of the QPSK signal is the same as in FIG. That is, such p-
Data and q-data are divided into "3H" section, "6" for each block.
When switching to the H "section and performing offset 4-phase differential phase modulation,
As shown in Fig. 4, for the "3H" section, the spectrum marked with ○ is for the section "6H", and the spectrum marked with ・ is periodically obtained for each block. The maximum amplitude at is the same level.

The above description is based on FIG. 8 in which the outputs p-1-data and q-1 of the D-FFs (32) and (34) of the differential encoder (30).
In the following description, the pilot data is differentially encoded with the initial data value being "0,0". Note that p-1
-Initial values of data and q-1-data may be "0,1", "1,0", and "1,1" in addition to "0,0", which will be described below.

When the initial value is “1,1”, the data obtained from the differential encoder (30) is −data and − in FIG. 2 and FIG.
As shown by the data, the p-data and the q-data are inverted by 180 °, respectively, but since the phase relationship does not change, the same effect as in the case of the initial value "0,0" is obtained. When the initial values are "0,1" and "1,0", the data obtained from the differential encoder (30) are p-data and -data and -data and q shown in Figs. 2 and 3, respectively. -It becomes data, and the phase relationship is different from when the initial value is "0,0" or "1,1". For example, in the case of p-data and-data, the data is 1 for the p-data in the "3H" section.
In the "6H" section, the phase relationship is advanced by 35 °, and the phase relationship is delayed by 135 ° with respect to p-data.
When such p-data and-data are modulated by the offset four-phase differential phase modulation, as shown in Fig. 4, the spectrum marked with "*" for the "3H" section and the spectrum marked with "○" for the "6H" section. Are obtained alternately. And-data and q
In the case of data as well, the same phase relationship is obtained, and the same effect can be obtained.

By inserting the <3H + 6H> type pilot data in the preamble and postamble positions as described above, the preamble and postamble positions are set. The two signals are recorded at the same level for each block, and the reproduction equalizer characteristic control unit (70) of the adaptive reproduction equalizer shown in FIG. It suffices to detect the peak value of the two signals and control the reproduction equalizer (50) so that the levels of the above two signals match.

BPR1 (71) of the playback equalizer characteristic control unit (70) has basically no spread of spectrum. There is little attenuation in the vicinity, and If the component of is attenuated to the extent that there is no problem in practical use,
In addition, BPF2 (72) There is little attenuation in the vicinity, and The accuracy of the pass characteristic may be comparatively loose, as long as it can be attenuated to such an extent that there is no problem in practical use. Further signal level detector DET1 (73), DET2 (74)
The operation of is also stable.

From the above, it can be seen that the <3H + 6H> type or <6H + CH> type repeating pattern is suitable for use in controlling the characteristics of the reproduction equalizer. Also, p data, q
The data is basically It is also useful for reproducing the data clock because it changes in the cycle of.

In the above embodiment, the repeating pattern is put in all of the preamble and the postamble, but it is put in only the preamble, only in the postamble, or in the preamble and a part of the block constituting the postamble. Needless to say, it is also good.

Further, in the above-mentioned embodiment, the data is switched every block, but it goes without saying that it may be more or less than that.

Further, in the above embodiment, the "3H" data string and the "6H" data string or the "6H" data string and the "CH" data string are used.
"3H" data string, "6H" data string, "CH" data string, "6H"
It goes without saying that it may be a cyclic data string consisting of a data string and a “3H” data string.

〔The invention's effect〕

As described above, according to the present invention, 1/8 of the data lock frequency FCL is centered on the carrier frequency of the PSK signal. It is possible to periodically generate QPSK signals with pilot signals of equal amplitude at. Pilot data combining "0011" type and "0110" type data strings, or "011"
Since the pilot data combining the 0 "type data sequence and the" 1100 "type data sequence is included in a part of the PCM signal, the spectrum shape of the reproduced QPSK signal can be easily detected without increasing the cost, and the reproduction equalization is performed. Optimal control of characteristics is facilitated.

[Brief description of drawings]

FIG. 1 is a diagram showing pilot data combining "0011" type and "0110" type for QPSK signal spectrum shape detection according to the present invention, and FIGS. 2 and 3 are serial parallel to the pilot data shown in FIG. FIG. 4 is a diagram for explaining the operation of the conversion and the differential encoder, and FIG. 4 shows an example of the spectrum of the offset 4-phase differential phase modulation signal when the offset 4-phase differential phase modulation is performed with the pilot data shown in FIG. Figure,
FIG. 5 is a block diagram showing the configuration of a conventional magnetic recording / reproducing apparatus, FIG. 6 is a diagram showing an example of a conventional format of an audio PCM signal, and FIG. 7 is a diagram showing an example of a conventional digital signal processing circuit. FIG. 8 is a diagram showing a conventional example of an offset four-phase differential phase modulation circuit, and FIG. 9 is a diagram for explaining the operation of a conventional preamble or postamble data “33H” and serial-parallel conversion and a differential encoder. Fig. 10 is a diagram showing an example of a spectrum of offset 4-phase differential phase modulation data for conventional preamble or postamble data, and Fig. 11 is a diagram showing an example of a spectrum of offset 4-phase differential phase modulation signal. Figures 12 and 13 show “33
The figure which shows an example of the spectrum of the offset 4 phase differential phase modulation signal with respect to a H "type data string and random data,
FIG. 14 is a block diagram of a conventional offset 4-phase differential phase demodulation circuit, FIG. 15 is a diagram showing an example of a spectrum of an offset 4-phase differential phase modulation signal during recording and reproduction, and FIG. 16 is a characteristic of a reproduction equalizer. FIG. 17 is a block diagram showing a configuration of a conventional adaptive reproduction equalizer, and FIG. 18 is a diagram for explaining a spectrum shape detection method of a reproduction equalized offset four-phase differential phase modulation signal. Is. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (3)

(57) [Claims] 1. A digital audio signal is converted into data corresponding to a video field, the digital audio data is offset four-phase differential phase modulated and recorded in a deep layer of a magnetic tape, and the video signal is frequency-modulated to produce the above audio signal. In a magnetic tape recording / reproducing apparatus configured to record and reproduce on a surface layer of a magnetic tape rather than data, the phase equalization means for reproducing and equalizing the phase-modulated digital audio data is equalized by the reproduction equalizer means. It is configured to be controlled by the spectral shape detecting means of the generated digital audio data to optimize the reproduction equalization characteristic of the reproduction equalizing means, and the operation of the spectral shape detecting means for a part of the digital audio data. In order to perform the
At least for the carrier frequency FC for phase modulation and the data clock FCL of the above digital audio data. Pilot data combining "0011" type data string and "0110" type data string, or combining "0110" type data string and "1100" type data string, which can alternately generate pilot signals with almost the same amplitude A magnetic tape recording / reproducing apparatus having at least one set of pilot data inserted therein. 2. The pilot data is "0011" type data string, "0110" type data string, "1100" type data string, "0110".
2. The magnetic tape recording / reproducing apparatus according to claim 1, wherein cyclic type pilot data, which is a combination of a type data sequence and a "0011" type data sequence, is inserted. 3. The magnetic tape recording / reproducing apparatus according to claim 1, wherein the pilot data is preamble or postamble data of the digital audio data.